1. Field of the Invention
The present invention relates in general to a method of manufacturing a fluid-filled elastic mount adapted to damp vibrations applied thereto, based on flows of a non-compressible fluid contained in the mount. More particularly, this invention is concerned with an improved method of manufacturing such a fluid-filled elastic mount, by which the filling of the mount with the fluid can be easily accomplished while assuring sufficiently high fluid tightness of the mount.
2. Discussion of the Prior Art
A cylindrical elastic mount is known as a vibration damping member interposed between two members of a vibration system for flexibly connecting these two members. The elastic mount includes an inner sleeve, an outer sleeve disposed radially outwardly of the inner sleeve, and an elastic body interposed between the inner and outer sleeves for flexibly connecting the two sleeves. This elastic mount is adapted to damp vibrations which are applied between the inner and outer sleeves primarily in a diametric direction of the mount. The elastic mount of the above type can be made small-sized or compact, and undergoes an effectively limited amount of relative displacement between the inner and outer sleeves when the mount receives an excessive amount of vibrational load. For this advantage, such an elastic mount is suitably used as an engine mount, a differential gear mount, a vehicle body mount and a suspension bushing for motor vehicles, for example.
In recent years, to meet an increasing requirement for higher vibration damping capability on motor vehicles with high performance, there is proposed a so-called fluid-filled elastic mount which is adapted to damp applied vibrations based on flows of a fluid contained therein. Examples of such an elastic mount are disclosed in laid-open Publications Nos. 63-172035 and 62-196434 of unexamined Japanese Patent Applications and U.S. Pat. No. 4,690,389. The elastic mount disclosed therein has a pressure-receiving chamber and a variable-volume equilibrium chamber which are formed between the inner and outer sleeves connected by the elastic body, and which are filled with a non-compressible fluid. Upon application of a vibrational load to the elastic mount, the pressure in the pressure-receiving chamber is changed due to elastic deformation of the elastic body. The equilibrium chamber is at least partially defined by a flexible diaphragm so that a change in the pressure of the chamber is absorbed or prevented by elastic deformation of the diaphragm. The elastic mount further has an orifice passage through which the fluid flows between the pressure-receiving and equilibrium chambers.
In manufacturing the fluid-filled elastic mount constructed as described above, it is necessary to fill the pressure-receiving and equilibrium chambers with the non-compressible fluid. Conventionally, diametrically opposite two pockets are formed in the elastic body, and the openings of these pockets are closed by the outer sleeve fitted on the elastic body, so as to provide the pressure-receiving and equilibrium chambers. The filling of the chambers with the fluid is effected by mounting the outer sleeve on the elastic body within a mass of the fluid, as disclosed in laid-open Publication No. 58-170608 of unexamined Japanese Patent Application. Alternatively, the filling operation is effected after the mount body is assembled so as to define the pressure-receiving and equilibrium chambers. In this case, the fluid is injected into the mount body, through a hole which is open to the pressure-receiving chamber and is formed through the outer sleeve, so as to fill with the fluid the pressure-receiving chamber, and the equilibrium chamber through the orifice passage. Thereafter, the hole formed through the outer sleeve is closed by or sealed with a closure member, such as a rivet.
In the former method described above, the fluid filling the elastic mount inevitably adheres to an outer surface of the mount while the outer sleeve is fitted on the elastic body within the mass of the fluid. Therefore, it is necessary to wash and dry the elastic mount after the filling operation, so as to remove the fluid from the surface of the mount. Thus, the known elastic mount is manufactured with relatively low efficiency.
The above problem is not encountered in the latter method in which the fluid is injected into the mount through the hole formed through the outer sleeve. However, it is necessary to form a recessed portion in the outer sleeve at which the injection hole is open, so as to prevent the rivet for closing the hole from protruding on the outer circumferential surface of the outer sleeve at which the mount is press-fitted in one of the two vehicle members to be flexibly connected. The formation of the recessed portion results in reduction in the mass of the elastic body and the volume of the pressure-receiving chamber, which leads to deterioration in the vibration damping capability and durability of the elastic mount. Further, when a considerably high pressure is developed in the pressure-receiving chamber upon application of a vibrational load, for example, the rivet or other similar closure member used for sealing up the injection hole is not capable of enduring such a high fluid pressure in the chamber, making it difficult to assure high fluid-tightness of the mount. Thus, the elastic mount produced according to the latter method is not satisfactory in terms of the durability and the operating reliability.